Audio signals were initially recorded as analog signals. An analog representation of an audio signal has a continuous nature (e.g., a smooth curving line), as opposed to a digital representation of an audio signal, which has a discrete nature. Each sample in a digital representation is a integer in base two, or binary, format, where each binary digit, or bit, in the integer is either a one or a zero.
It is difficult, if not impossible, to copy or transmit an analog representation of a signal perfectly, whereas it is easy to do the same for a digital representation of a signal. Any deviation in an analog representation of an audio signal as compared to the original signal represents loss of audio quality. Since digital representations of audio signals can be copied or transmitted perfectly, it is the preferred representation for audio signals.
There are many different formats for digitally representing an audio signal. The essential characteristics of a digital representation is its encoding scheme (e.g., μ-law (pronounced mu-law), a-law), the integer of bits that represent each sample in the signal (e.g., 8-bit, 16-bit, 32-bit), and the sampling rate per second used to digitize the signal (e.g., 8 KHz, 16 KHz, 32 KHz). The integer of bits that represent a integer is commonly referred to as the word, byte, or block length.
With audio signals increasingly being included in computer communication, different file formats have arisen. Some file formats are self-describing. That is, they include header information that says what digital representation was used to encode the audio signal. However, header information is not always accurate. Other file formats, referred to as headerless formats, do not say what digital representation was used to encode an audio signal. Such formats can be difficult to decipher, and may require one to listen to the audio file.
Computer files include extensions. For example, a file named filename.ext, has “.ext” as its file extension. The most common file extension on the INTERNET include .snd, .au, .aiff .wav, and .mov. The .snd extension is ambiguous because it could indicate the self-describing format of a Next Computer or the headerless format of an Apple Macintosh computer. The .au format is used in SUN Microsystems computers to indicate μ-law encoding. The .aiff format is used in Apple Macintosh computers. The .wav format is used on computers running the Microsoft Windows operating system. The .mov format is used in QuickTime movies. The extension is supposed to indicate the format used to encode the file. However, just as headers in self-describing files do not always describe the file format used, neither do file extensions.
U.S. Pat. No. 6,285,637, entitled “METHOD AND APPARATUS FOR AUTOMATIC SECTOR FORMAT IDENTIFICATION IN AN OPTICAL STORAGE DEVICE,” discloses a method of distinguishing between the formats for Compact Disc-Read Only Memory (CD-ROM) and Compact Disc-Digital Audio (CD-DA) on an optical storage device by examining a Q-channel data-type indicator bit. The value of the bit indicates whether the format of the optical storage device is CD-ROM or CD-DA. The present invention does not examine a Q-channel data-type bit to determine format as does U.S. Pat. No. 6,285,637. In addition, U.S. Pat. No. 6,285,637 does not disclose a method of distinguishing between digital audio formats as does the present invention. U.S. Pat. No. 6,285,637 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,483,988, entitled “AUDIO AND VIDEO SIGNALS RECORDING APPARATUS HAVING SIGNAL FORMAT DETECTION FUNCTION,” discloses a method of determining if received audio is in AC-3 format (i.e., Digital Dolby) or in a format supported by MPEG by extracting bit stream and header information. The present invention does not use header information to determine digital audio format. U.S. Pat. No. 6,483,988 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,918,554, entitled “TAPE CARTRIDGE FORMAT IDENTIFICATION IN A SINGLE REEL TAPE HANDLING DEVICE,” discloses a method of identifying the format of a tape by including information on a tape cartridge leader that indicates the format of the tape. The present invention does not use information of a leader of tape to determine format as does U.S. Pat. No. 6,918,554. U.S. Pat. No. 6,918,554 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,999,827, entitled “AUTO-DETECTION OF AUDIO INPUT FORMATS,” discloses a device for distinguishing between two different digital audio formats, 12S and SPDIF, by detecting edge transmissions and using a time counter to determine the time slot of the received signal. A time slot for 12S is in the range from 81.38 nanoseconds to 488.28 nanoseconds. A time slot for SPDIF is in the range from 5.2 microseconds to 250 microseconds. The format for whichever range encompasses the time slot determined by U.S. Pat. No. 6,999,827 is determined to be the format of the received signal The present invention does not use edge detection and time slot estimation to determine format as does U.S. Pat. No. 6,999,827. U.S. Pat. No. 6,999,827 is hereby incorporated by reference into the specification of the present invention.
JSTOR and Harvard University Library collaborated to develop a framework for format validation of various digital objects. JSTOR is a not-for-profit organization that maintains an archive of important scholarly journals. The framework that was developed is called JHOVE (pronounced “jove”), which stands for the JSTOR/Harvard Object Validation Environment. JHOVE identifies the format of various self-defining digital formats by determining whether or not the signal is formed according to the requirements of a particular digital format (e.g., does the signal contain a required integer at required byte offsets, does the signal contain all of the required components, does the signal include any components that it should not, etc.). The present invention does not determine format by determining whether or not the signal is formed according to the requirements of a particular digital format as does JHOVE. In addition, JHOVE cannot identify a headerless digital format as does the present invention.
There is a need for a method of identifying digital audio formats, whether self-defining or headerless. The present invention is such a method.